Direction finding system



Feb. 19,1935.

H P. THOMAS DIRECTION FINDING SYSTEM Filed Oct'. 26, 1932 Ping. 5.

Q Fig. 5

"H lll l Inventor Henry 1. Thpmas,

lea I-Iis Attofneg.

Patented Feb. "19,; 1935 I UN ED j. ST

j lint-E01nosmmmc sYsrEM V V "Henry P .;Cihomas, schenectadyg Nrfaassignor to General Electric Company-,aporporation of New york IApplicationclimber-"12c; .1932, Serial Na. 63:);592' I a iMClaims. (01.250 4101 .Myirivention relates toreceiv'ing systems and moreparticularly to systems used for direction finding; radio courseindicating and the like;

. P substantially. instantaneously responsive" nonlincar resistor" isdescribedin U. '8. Patent No.1 ;822,742 issued to'fKLB. McEachron,ahd iscommercially know n'as Thyrite.. This-resistor iscoinposed of a dense,homogeneouainorganic compound of ceramic material; and a has thel0"-characteristic thatwhen placed in circuit with a source of potentialits resistanceialls Wlthincrease of potential in the/circuit. This char-I acteristic of thef'icurrent and resistance can 1 be expressed the formof .'a' simple. hyperbolic I I is the density of current'in amperes; Cis a con- "stant andthe'exponenta is the" slope of'the curve representedbythe equation when plotted with respect to logarithmic coordinates. Theex-i *ponent a is less than unityfan'd the constant C may preferablyvary'betweenlO and'600. This material also has the' peculiarproperty ofreacting substantially"instantaneously to. asymmetr'i-' f ca1 voltage orcurrent wave shapesso that a por mm of-such waves isf-rectifiedandadirect current'flows in the circuit; butwhensymmetrical Waves arepassed-through it'no direct current flowoccurs: The direction of thedirect current now due to the partial rectification o fraisymid-"metrical wave shapesi s' dependent upon whether themaximum'peakofthe asymmetrical wave is positive ornegati've. g

It is object of my invention to utilize such (a non-linear resistor inaradio receiver circuit.

35- "It is a further object of myinvention to provide a radio receiverutilizingfa non-linear resistor to produce reliable direct nullindications for direction, or course, finding purposes.

. r A further object of my ihvention'isto provide transmitter fortransmitting different direc:

tions a plurality of waves each modulated with, a plurality oflowfrequency currents; all having:

.a predetermined-phase relation toeach other. i

A still further objectuof my invention is to providea radio receiverhaving anon-linearresistor circuit for producing a distinctive responseto the phase relation between currents having. a

5o phase relation determined by-theposition-of the radio receiver withrespect to a radidtransmitting station.

A further object of my-invention is to provide a radio receiver having acircuit with non-linear characteristicresponsive to phase differencesfbewhere R is the resistance,

tions thereof.

aradio be'acon course system having a beacon tween the modulations onplurality of carrier"; Waves and a harmonic of such modulations.

A further object of my invention is to' provide a'radio beacon coursetransmitter and areceiterY '7 cooperatingtherewith" having meansincluding 5 such a non+linear resistor for indicating courses" otherthan'those' formed by the directive tran sy flm'issions ofthetransmitter.

The novel 1 features which I believe to be charsacteristic ofmyinvention are set forth withpar: e; 7

they combine in a receiver'embod-ying my inven-- tion. Fig; 2illustrates an embodiment;of myfinvention and Figs. 4. and 6 illustratemodific'a Referring to Fig. 1, I have-illustrated-"an arr-25tennapattern which results froi'n' loop 3 ntenn arranged atjright anglesto each other; The} pattern A-is the Figure S'ra'diation pattern "of oneloop antenna and the pattern 'B is theFigu're' 8 radiation pattern ofa'seco'nd loop antenna.f These two patterns cooperating together providefour radio beacon courses 'shown as "DC, OD; OE and'OF. Intonearrangementthe carrienw'av'etransmitted in the pattern A maybe inthe'form of a plura'litvofdots 'separated jby -long time intervals. .Thecarrier wave transmitted in'the pattern B will constitute'a series'ofdashes'equaL to-1the timeintervals between the dotstransmittedafrom' thepattern A. Along' any one of, v the courses such. as DC the. intensityof the" 40" radiations receivedfrom :the' patterns AB willbe equal,"thus producing'in the receiver a constant carrier current; Any deviationfrom a course such as 0C will" prodiiea variation-in g the amplitude of7 the carrier received; and "hav ing an envelope whichha's a shapedependent 1 upon whether thereceiver is to the right or -leftofthe'course OC. This envelope-of the car'rier will produceintheoutput-circuitofthe receiver;

an asymmetrical audio-frequehcy wavei This 'ofl audio frequency wavemaybe' utilized to give an-indication t6 the pilot of'a rnobile craftas twhether he is to the right drIefE of -the pred termined course O'C.-

As analterhative method} tl'ie carri e r waive ra diated from thepattern A may be constant and modulated by a plurality of audiofrequency waves as, for example, a fundamentalwave and a harmonicthereof having a definite phase relation with respect to the fundamentalwave, as expressed by the equation B(sin wt-K COS'Zw'i; wherein B and Kare constants, w is 27), 1 being frequency in cycles persecond and t istime in seconds. The wave radiated from the pattern B is modulated by aplurality of similar audio frequency waves as expressed by the equationB(sin wt-l-K cos 2wt) Thus areceiver on a mobile craft moving along theline QC will receive equal intensities from the patterns A and B and theaudio output from the receiver will" be B(sin ot.K cos 2 wt) +B(sinwt+Kcos 2 wt):

'2B(sin wt). In other words, the second harmonic of the fundamentalmodulation wave cancels out and the simple sine wave will be present inthe output circuit when the receiver is on the course QC. If the craftdeviates from the course 00, the harmonic. of thefundamental'modulation'received from one of the patterns willpredominate in the resultant equation and thus the fundamental and saidsecond harmonic will be present in the outputcircuit of the. receiver. a

In Fig. 2 I have illustrated a receiver arrangement embodying myinvention Iwhich may be utilized for receiving the waves transmitted bya radio beacon having a field pattern such as is i1- lustrated in Fig.1, and this receiver arrangement will respond to'either typeof carrierwave transmission. The antenna 1 is connected to a suitable receiver 2.The receiver 2 may comprise a radio frequency amplifier, a detector, anaudio frequency amplifierand an output transformer, or the detector maybe followed by a direct current amplifier and an output transformer. Thepurpose of this arrangement will become apparent later. Theoutput'circuit of the receiver is provided witha non-linear resistor 3and a zerocenter direct current meter 4. The non-linear resistor 3 ispreferably of the type described in 'U. S. Patent No. 1,822,742 issuedSeptember 8,

1931, to K. B. McEachron, but may be composed of any other material orcombinationof elements which will provide the desired non-linearresistance-current characteristic. An example: of such arrangement wouldbe two copper oxide rectifiers of the type described in'U. S. Patent No;1,640,335 issued August 23, 1927, to'Lars O.

, Grondahl, which are connected in parallel and arranged opposite toeach other so as to produce.

a bi-laterally conducting path.

While the output transformer is not'essential to the receiver 2, its useis desirable as it eliminates the direct'current component which isusually present in the anode circuit of the output tube. The eliminationof the direct current component in the output circuit of the receiverwhich contains the non-linear resistor3 and-the'zero-center directcurrentmeter' l, permits the use of a more sensitive direct currentmeter than'would be the case if the direct currentcomponent were 75;.and aharmonic thereof havingapredetermined present.

;along the various beacon courses.

.When the receiver disclosed in Fig. 2 is utilized in connection with aradio beacon ofthe type referred to in connection with- Fig. 1 whichtransmits carrier waves modulated by a' fundamental phase relation tothe fundamental, the output circuit of the receiver 2 will have a simplesine wave therein when the receiver is upon the source 0C. If thereceiver, however, has deviated from the course 06 the fundamentalfrequency and a portion of one of the harmonic frequencies will bepresent in the output circuit. If a wave of the form Eiisin wt) i E2(C0s2st) is present in the output circuit impressed upon thenon-linearresistor 3, the behavior of the resistor will be such that, if theexponent a equals in the equation R=CI, there will be a direct currentflowing in the circuit which is of the magnitude er the deviation fromthe course 0C is to the right or left of the course. The receiver willact similarly along thecourses OD, OE and OF.

When the receiver shown in Fig. 2 is usedwith a beacon of the type whichtransmits carrier waves which are interrupted so as to produce 00-operative carrier waves in the section on the courseOC, the operation ofthe receiver will be as follows: Along the course 00 the intensities ofthe carrier waves received from the patterns 7 This asymmetrical waveshape of the envelopewill be transmitted to the output circuit of thereceiver 2 by the action of the detector and the output. transformer asan asymmetrical audio frequency wave. This asymmetrical audio frequencywave will be acted upon by the non-linear resistor 3-to produce a directcurrent which will actuate the zero-center meter 4 to give an indicationto the pilot of the mobile craft that he has deviated to the right orleft of the course 00.

The operation ofthe'receiver under this condition may be betterunderstood by reference to Fig. 3 in which the curve U illustrates thecarrier 'requene-y impulses tern A; and the curve V illustratesthecarrier ransmitted within the pat- 7 frequency impulses transmittedwithin the pat tern B. A deviation to the right of the course 0C, forexample, may produce a wave such as shown in curve W, whereas adeviation to the left of the course 00 will produce a'curve such asshown at X. A carrier wave such as W will be changed by the action ofthe detector and the output transformer of the receiver 2 to produce anaudio frequency wave such as shown atY, and a carrier wave such as shownat X will be changed a by the detector and the output transformer of theclearness but it will be understood that waves similar to these will beproduced by the detector and the output transforrner when the envelopeof carrierwaves such as W and X is suiiiciently although the amplitudeofthenegative half of r amplifiedf The outputtransformer eliminates thedirect current component present in the output rcircuit. of. the outputtube, and the inherent action of'a transformeris such-thatlthe positivea and negative areas of waves'such 'as X and Z aremaintainedfiequalwThus, for examplegin an audio frequency wave such asuYthe positive and negative areas of the halves of the Wave are equal,

the wave isvconsiderably greater than the positive half or the wave. Theasynnnertical audio frequency' waves such asshown r'at and Z will beacted upon'by the non-linear resistor Bto produce direct currentcomponents in'o'ne direction or theother which will actuate the'zero-center meter 4 to the right orleft. iv

:If the receiver 'inFig. 4 be used'with a 4 eourse radio beacon of thetype referred to inconnecreceiver 2 which is provided with adetectonaudio and radio frequency amplifiers and an output transformer.The output circuit of the radio receiver 2 comprises two branchcircuitsone'of which "is connected through a non-linear resistor 5 to oppositepointsjofla bridge 6; The bridge 6 is composedof'four resistors 7, 8, 9and 10;- ?The 1 other branch of the output circuit is connected throughan audio frequency transformer 11 to a full-wave rectifier circuit; -12.This full-wave rectifier circuit maybemade up ofany suitable rectifiersbut; is preferably composed of'foxide rectifiers of the type describedin the U. S. Patent No. 1,640335 issued August.23;,- 1927, to Lars O lGrondahl: The output of this rectifier circuit is connected through anon-linear resistor 13 to the oppositeisides of the bridge 6." Azero-center direct current meter l4is connectedb'etween the resistors?and why means of adjustable contacts.

The rectifier- 12- produces l a current which i is proportionaltor thecube ofthe voltage present in the output circuitsof the receiver 2. If,the cur In these equations I is t 5 harmonic frequency;

rent produced by the rectifier 12 and the current 7 flowingvthrough' thenon-linear resistor 5' are combined in the bridge circuit 6,a zeroreadingof the direct current meter 14 indicates a definite ratio ofrthetwo currents which may be expressed by i the; following equations:I1=K1E1 E2 :which is *equal to the current flowingthrough the nonlinearresistor 5; and Iz='K1?E 1 which is approximately equal to-the currentflowing through-the other non-linear resistor 13.1 From thi s'we obtainhe current, K isa constant, E1 is the voltage component ofth'efundamental frequenc'y'andiEz is the voltage component ofjthe tingof the contactsionthebridge circuit at which no current flowsthrough themeter indicates that a definite proportion of the second'harmonic ofthelmodulations, is being received;- The bridge arrangement fi-mayr havethe contacts of the meter 14 soadjusted that themeter' 14 will read zerofor an' 'angle ata-certain number of degrees tea-course such as 0C; thusenablingthe craftto I follow a course such as 0G.

rang. 5 Ihave indicated the field patte'r n of Thus" one particularxsetefollowingtheproper course. r 7 While I have shown and described myinvention in connection with certain specific embodi- 3: af radib'beaconcomprising thr'ee loop antennae arranged at angles: of 60 to each other.These antennaatransmit carrier currents which are modulated by audiofrequency currents similar to those described in connection with thebeacon in Fig.:.l.- 'The modulation of the three'antenna maybe expressedby the following equations: Afis inwt-i-sin Zwf); A(sin (wi+12() +Sin'Zwt); A sin (wt+240)+5l11 2M); wherein A isa constant; a is 211, fbeing the'frequency; and t is the time. A-carrierwavehaving oneofthesemodu lations is transmittedfrom each of the loop The antennaepatterns'as indicated at, H, I, 5. output of. a receiver traveling on one of thecourses determined by these "field-V patterns will now consist of twofrequencies of practically con- 1 stant amplitude but with the phaseangle between' them a function of'the position of the receiver withrespect to the beacon transmitter. As the receiver makes a completecircuitaround the transmitter, the phase of the fundamental frequency inthe output circuit of the receiver shifts two cycles of. the fundamentalwith respect to the i secondharmonic frequency. When-the two waves areiii-the samephaseor 180 out of phase, 'the resultant 'wave in the outputcircuit or the receiver will 'besymm'etrical and therewill be no jdirectcurrent flowing through the meterli This willoccur' eight times aroundthe circuit or :inlotherwords, the=courses are at an angle of [45 toeachother Y I b 'Any one of the eight courses may be-followed by-facraft provided with areceiver such as dis-i closed in'Fig. 2. Coursesother thanthe eight provided by the beacon may be flown by utilizing areceiver suc h as disclosed-in Fig. 6. The retenna 1 connected to areceiver 21 which has a circuit between the] receiver and a non-linearresistor 3 and a zero-center direct current meter 4. The phase shiftingdevice 15 :operates to ,ceiver arrangement in Fig; 6 comprises an anaphase shifting device15 connected inthe output shift the phase'relationbetween the two frequen- I ciespresent in the output circuit'before theyare impressedupon' the non-linear resistor 3.

By adjusting thephase shifterjthe phases of the two frequencies can beshifted so that it is possible'to travel on'any desired" course. 'tionfrom suchfa course, however, will produce A deviaan asymmetrical voltagein the output circuit which contai' s a non-linear resistor 3 becauseof'thepresence of harmonic currents having a phase relation-to thefundamental other'thanzero or 180. 7 I

The receiver arrangements disclosed in'Figs.

ratus in the output circuit of the receiver 2 and substitutetherefor atranslating device such'as a pair of headphones, thereby to utilize thereceiver for the reception of communication.

My invention has the further advantage of being inexpensive and at thesame time providing anarrangerne nt'wherein the indicating meter atits'null position indicates that "the'craft is merits it will, of course,be understood that I do 2,4 and 6 may utilize any other suitable non-flinear resistor or combination of elements having the properresistance-current characteristic; It is furthermore possible to'disconnect the appa not wish't o be limited theretogsince it is apparentthat the principles herein disclosedare's'uscep V tible to numerousother applications, and modi- "iic'ationsj may be;- made :in -,thecircuit arrang plied, and means movable in a radio field to conmeritsand in the instrumentalities employed without departingfrom the spiritand scope of my invention as set forth in the appended claims. WhatIclaim as new and desire to secureby Letters Patent of the United Statesis: 1. The combination in a radio receiving system, of meansforproducing; an=electromotive force having an asymmetrical, wave formdependent, upon received radio waves, a non-linear resistance, and meansto impress said asymmetrical wave on saidresistance thereby to produce aunidirectional electromotive force having a polarity dependent upon theasymmetry of the wave form produced.

2. In a radio receiver, the combination of'means controlled by receivedradio waves for producing oscillations having asymmetrical wave formsand means forreceiving said oscillations, said latter means including asubstantially instantaneously responsive non-linear resistor whereby adistinctive response in accordance with the asymmetry of said wave formis produced.

3. In a radio receiver, the, Combination of' a non-linear resistor, andmeans for producing os-. cillations having asymmetricalwave forms andforsupplying said oscillations to said 1esistor,: the asymmetry of saidwave forms being con trolled by received radio waves, said non-linearresistor havinga characteristic represented by the equation R=CI- whereR, is the resistance, 1 is the density of current per square inch, C isa constant and a' is the slope of the curve represented by said equationwhen plotted with respect to logarithmic coordinates.

4. The combination, in a radio receiver, of a bilaterallyconductivenon-linear resistor, means for supplying to said non-linear resistor anelectromotive force having either of two different typ s of oppositelyasymmetrical wave forms whereby a unidirectional current flows throughvsaidresistor having a polarity dependent upon the wave form of theelectromotive'force suptrol said first means to determine in accordancewith the position of saidmovable means the type of wave form of theelectromotive force supplied to said non-linear resistor, M

5.'The combination, in a radio course finding systemfor moving bodies,means on said body to produce a plurality of periodically varyingcurrents, having a phase relation dependent upon the position of saidbody with reference to a predetermined course, a, non-linear resistance,means to pass said current through said nonlinear resistance thereby toproduce a unidirectional current through said resistance having polaritydependent upon the posit-ion of said body with reference to said course,and means responsive to the polarity of said current.

6. Ihe combination, in aradio receiver, of a circuit, means forsupplying said circuit with a plurality of periodically varying currentshaving a phase relation therebetween determined by the position of saidradio receiver with respect to a transmitting station to which saidreceiver responds, and means comprising, a' non-linear resistor forproducing a direct ciu'rent component in said circuit in response tosaid phase relation, and a device connected to said circuit andenergized responsively to said direct current. component. I I

'7. The combination, in a radio receiving system having a transmittingstation and a re- 'ceiver, of a circuit, means for supplying saidcircuit withja pluralitygofalternating currents directive antenna arransaid fundamental and harmonics from a predetermodulated with afundamental wave and a harhaving a phase relation variable dependentupon the position of the-radio'receiver with respect to a transmittingstation, means comprising a nonlinear resistor device responsive tovariations in said phase relation for rectifying said currents, andconnections from said circuit to an indicating instrument.

8.,A radio course, beacon system comprising in combination means forradiating carrier waves in different directions, means for modulatingeach ofsaid carrierwaves with a plurality of low frequency waves, eachofsaid low frequency waves having a predetermined phase relation to: eachother, a radio receiver responsive to said carrier waves for reproducingsaidlow frequency waves, means in said radio receiver for shifting thephase of certain of said low frequency waves with respect tothe otherwaves of different frequency, and means'responsive to the resultantphase relation'of said low frequency waves for producing an indication;

9. A radio beacon system including a beacon transmitting station havinga plurality of directive antennae arranged at equal angles to eachother, means forgenerating a plurality of low frequency waves having afundamental low frequency and a-harmonic of said fundamental, saidharmonic frequencies all being in phase and said fundamental frequencieshaving a predetermined phase-relation to the harmonic frequency and toeach other, means for generating a plurality of carrier waves andmodulating each of said carrier waves with oneof said fundamental andharmonic frequencies, means for radiating each modulated carrier wavefrom oneof said antemiae'to produce a plurality of radio beacon courses,a carrier wave detector arranged to receive said car-- rier waves,whereby modulated carrier waves received'in said detector cooperate toproduce in said detector a symmetrical low frequency wave when saidreceiver is uponany of said courses.

10. A' radio beacon system comprising three ged at equal angles to eachother,;means for generating a plurality of. like carrier waves, meansfor modulating each of said carrier waves with a, fundamental lowfrequency and aharmonic thereof, said harmonic frequencies all beingin'phase and said funda-' mental frequencies being'displaced in phase anequal-amount with respect to each other and means-for transmitting saidmodulated carrier waves'w'nereby eight beacon courses are obtainedwherein the resultant fundamental and harmonic frequencies are in thesame phase or 180 out of phase. 1

11. The combinatiomof a high frequencyre-' ceiver adapted for receptionof a carrier wave modulated with a fundamental wave and a har-' monicthereof, means for indicating variations-f mined ratio of intensities,and ing said predetermined ratio.

12. The combination, of a high frequency re-s I ceiver adapted forreception of a carrier Wave means for adjust monic thereof, an outputcircuit for said receiver, and means connected in said output circuitfor producing distinctive --indications upon variation of saidfundamental J and harmonic in opposite senses from a predetermined ratioof intensities.

13. Th'e combination;ofa high frequency receiver adapted for receptionof a carrier wave modulated with a fundamental wave and a harmonicthereof, means for indicating variations of. said fundamentalandharmonics from a predee 7 1,991,476 termined ratio ofintensities,*and means for ad justing said predetermined ratio, means insaid output circuit for adjusting the phase relation between saidfundamental and harmonic, and' indicating means responsive to said phaserelation.

14. In a radio beacon system; means for radiating waves of the samefrequency in each of a plu rality of difierent directions,- the Wavesradiated in the different directions being displaced in phase relationsbetween said fundamental and harmonic Waves to determine the position ofthe movable body. r

HENRY P. THOMAS.

